This invention relates to a triggering circuit for use in an aerosol drug dispensing device, and in particular, to a triggering circuit for detecting the operation of the device by a user.
Prior trigger circuits do not readily discriminate between a real triggering event, i.e. a patient inhaling on the device, and a false event, i.e. the movement of the device through the air or changes in ambient conditions. If the circuit were to be triggered by a false event, the device would be operated when the user was not ready to receive the drug and therefore that dose of the drug would be wasted. Thus, the present invention aims to provide a control circuit which overcomes the above problem.
WO92/07599 discloses a portable inhalation device for the administration of medicament in the form of aerosolised fine particles or droplets of liquid to the respiratory system of a patient. The inhalation device comprises a bridge circuit which creates an electrical output signal dependent upon the resistance in a hot wire anemometer. The resistance of this element varies as the flow across it changes and accordingly, the bridge circuit is not self nulling.